Iran's opposition movement is holding what is being described as a "silent memorial" to remember the victims of the unrest that erupted following last month's contested presidential election. The Iranian government banned the gathering, leading to fears of more violence.

Iranian security forces are once again clamping down hard on an opposition demonstration in a Tehran cemetery called to honor those slain during weeks of unrest, following the June 12 election.

A video, posted on opposition leader and presidential candidate Mir Hossein Mousavi's Facebook website showed scores of demonstrators waving the "V" for victory sign, and chanting "Mir Hossein", as they faced off against riot police.

An Iranian émigré radio station in Los Angeles, spoke with a man who said he was at the demonstration, and indicated opposition leader Mir Hossein Moussavi had visited the cemetery before being escorted to his car by police.

Another man, who said he was at the cemetery, told an Iranian opposition website that police were chasing young people who were chanting "death to the dictator", while others were "throwing flowers at the police, asking them to support them."

According to émigré radio, Ayatollah Karroubi told supporters at the cemetery to head towards Tehran's Grand Mosalla mosque, where a mourning ceremony had originally been planned.

On their websites, Mr. Moussavi and Ayatollah Karroubi urged supporters to go ahead with the planned "silent memorial", despite being refused permission for the gathering by Iran's interior ministry.

Thursday marks the 40th day after bloody and bitter clashes between demonstrators and police, in which many were killed or wounded. The 40-day anniversary of a death is traditionally used for mourning, in Islam.

Opposition supporters also prepared a video, set to music, on Mr. Moussavi's Facebook website, honoring those slain during weeks of unrest and clashes with police. It showed demonstrators covered with blood and others writhing in pain after being shot by police.

Iranian government TV ignored the protests, talking instead about the upcoming August 3 inauguration of incumbent President Mahmoud Ahmedinejad. He was officially credited with 64 percent of the vote, amid charges of widespread vote-rigging.